Nanotribology of biaxially oriented poly(ethylene terephthalate) film

Repeated scanning of biaxially oriented poly(ethylene terephthalate) (PET) film surfaces in contact mode scanning force microscopy leads to sample wear. At low to moderate loads (<50 nN) well-defined ridges are formed. The dimensions and the separation of these ridges are determined by the scan parameters. The ridge spacing and the root mean squared (rms) roughness of the surface increase with the load, and appear to exhibit power law relationships. At low forces, material is not displaced from the scan area, but as the force is increased, increasing amounts of material are displaced to the periphery of the worn area. At high forces the surface disruption is extensive. The evolution of sample damage is not influenced by the scan rate, but is strongly influenced by changes in the number of scan lines, indicating that wear is a cumulative process, accelerated when the spacing between scan lines is small compared to the tip radius.